The present invention relates to a method of producing a copolymer that is preferably used in a production of a photographic copolymer.
That copolymer couplers that are made nondiffusible are effective in photographic light-sensitive materials is described, for example, in JP-A-57-94752 (xe2x80x9cJP-Axe2x80x9d means unexamined published Japanese patent application), JP-A-58-224352, and JP-A-58-28745, and they are put to practical use in commercially available current photographic light-sensitive materials.
In the production of these copolymer couplers, a solvent in the polymerization reaction has been studied. For example, ethyl acetate has been useful as a solvent in the polymerization reaction. In the production from a monomer low in solubility, however, there has been the problem that the reaction concentration is lowered and the polymerization time is prolonged. In contrast, it has been found that dimethylene glycol (DMG) is higher in solubility than ethyl acetate, and that the use of DMG can shorten the polymerization time.
It should also be noted that, in the production of conventional polymer couplers, to separate the copolymer coupler after the polymerization reaction, a large amount of water is needed for the reprecipitation. That, however, involves a problem of waste liquid or the like in the reprecipitation using a large amount of water, a problem of the load of drying the copolymer coupler, a problem that production facilities cannot be used easily in common, and a problem of the cost. Therefore the reprecipitation step is a step to be avoided if possible. As an alternative method thereto, a flash vacuum dry system (hereinafter referred to as FVD, in some cases) is proposed (e.g. JP-A-2-191501). In this system, a solution containing the substance to be dried is heated and concentrated in a long pipe-type steam heating pipe, to be formed into a solid/gas mixture of a powdery dried substance and a gas, and then, the solid/gas mixture is spouted into an atmosphere having a reduced pressure, to separate the powdery dried substance from the gas, to obtain the powdery dried substance. In this system, however, if an ether-series solvent, such as DMG, is used, a risk that the formation of a peroxide in the processing by the FVD will lead to inflammation (self-ignition) or the like is feared, and there arises a problem that the spray nozzle at the time of processing (concentrating) by the FVD is clogged.
Therefore, an object of the present invention is to provide a production method that can give a copolymer high in solubility and suitable for FVD processing, and the method is excellent from the standpoint of the production capacity and stable/safe production throughout the process.
Further, another object of the present invention is to provide a production method capable of giving a photographic copolymer coupler that is excellent in photographic performance. In particular, still another object of the present invention is to provide a method for producing a copolymer coupler that makes it possible to form an image excellent in gradation, antifogging, etc., in color photographic light-sensitive materials.
Other and further objects, features, and advantages of the invention will appear more fully from the following description, taken in connection with the accompanying drawing.